The present invention relates to an electrochromic display device and, more particularly, to a display electrode structure in an electrochromic display cell.
When an electrochromic display electrode in an electrochromic display device has a large size, the display electrode is gradually colored from the edge portion thereof upon application of a coloration signal. This is considered to be caused by variations of electric field density distribution. Therefore, the conventional electrochromic display device was not suited for displaying a large pattern. Moreover, the conventional electrochromic display device required a considerably long period coloration signal in order to obtain uniform coloration in a large size segment.
The present inventor has discovered, through experimentation, that the above-mentioned gradual coloration is visually observed when the electrochromic display layer has a size larger than 0.1 cm.sup.2.
Accordingly, an object of the present invention is to provide an electrochromic display cell which has a novel electrochromic display electrode suited for displaying a large pattern.
Another object of the present invention is to obtain uniform coloration of an electrochromic display segment in a short period of time.
Still another object of the present invention is to enhance the visibility of a displayed pattern in an electrochromic display device including a WO.sub.3 film formed on a display electrode.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, an electrochromic layer comprising a plurality of electrochromic segments (WO.sub.3 layers) are formed on a transparent display electrode which receives a coloration signal and a bleach signal for displaying a desired pattern. That is, the electrochromic layer formed on the transparent display electorde is divided into a plurality of segments so that one electrochromic segment has a size smaller than 0.1 cm.sup.2. A thin gap formed between adjacent electrochromic segments has preferably a width of about 100 .mu.m through 200 .mu.m.